Method of making a composite electric machine rotor assembly

ABSTRACT

A method of making composite electric machine rotor assembly of a desired magnetic pattern. Magnetic segments and non-magnetic segments are separately formed to green strength, and then arranged adjacent to each other in a desired magnetic pattern. A small amount of powder material is added in-between the segments, and the whole assembly is then sintered to form a sinterbonded composite component of high structural integrity.

CROSS REFERENCE TO RELATED DOCUMENTS

This application is a Division of U.S. application Ser. No. 10/123,804,filed on Apr. 16, 2002, with U.S. Pat. No. 6,889,419.

FIELD OF THE INVENTION

This invention relates generally to composite electric machine rotorcomponents and rotor sense parts, and more particularly, to themanufacture of rotor components and rotor sense parts by sinterbonding.

BACKGROUND OF THE INVENTION

It is to be understood that the present invention is equally applicablein the context of generators as well as motors. However, to simplify thedescription that follows, reference to a motor should also be understoodto include generators.

In the field of electric machine rotor cores, stator cores andgenerators, the machine cores are typically constructed usinglaminations stamped from electrical steel. The laminations are stackedand pressed onto a shaft. Then, in most electric machines, windings orpermanent magnets are added. These laminations are configured to providea machine having magnetic, non-magnetic, plastic and/or permanent magnetregions to provide the flux paths and magnetic barriers necessary foroperation of the machines. When the shape of the laminations and/or theadditional winding/permanent magnet components are compromised, reducedoperating speed and flux leakage may occur, thus limiting performance ofthe electric machine. By way of example, synchronous reluctance rotorsformed from stacked axial laminations are structurally weak due toproblems associated both with the fastening together of the laminationsand with shifting of the laminations during operation of their manycircumferentially discontinuous components. This results in adrastically lower top speed. Similarly, stamped radial laminations forsynchronous reluctance rotors require structural support material at theends and in the middle of the magnetic insulation slots. This results inboth structural weakness due to the small slot supports and reducedoutput power due to magnetic flux leakage through the slot supports.There are various types of machines utilizing rotors that requirenon-magnetic structural support, including synchronous reluctancemachines, switched reluctance machines, induction machines, surface-typepermanent magnet machines, circumferential-type interior permanentmagnet machines, and spoke-type interior permanent magnet machines. Eachof these machines utilize rotor components or rotor sense rings ofcomposite magnetic, non-magnetic, plastic, electric and/or permanentmagnet materials that suffer from the aforementioned problems.

Despite the aforementioned problems, and the general acceptance ofconventional lamination practices as being cost effective and adequatein performance, new powder metal manufacturing technologies cansignificantly improve the performance of electric machines by bondingmagnetic (permeable) and non-magnetic (non-permeable) materialstogether. Doing so permits the use of completely non-magnetic structuralsupports that not only provide the additional strength to allow therotors to spin faster, for example up to 80% faster, but also virtuallyeliminate the flux leakage paths that the traditionally manufacturedelectric machines must include to ensure rotor integrity, but which leadto reduced power output and lower efficiency.

Powder metal manufacturing technologies that allow two or more powdermetals to be bonded together to form a rotor core have been recentlydisclosed by the present inventors. Specifically, the followingco-pending patent applications are directed to composite powder metalelectric machine rotor cores fabricated by a compaction-sinter process:U.S. patent application Ser. No. 09/970,230 filed on Oct. 3, 2001 andentitled “Manufacturing Method and Composite Powder Metal Rotor Assemblyfor Synchronous Reluctance Machine”; U.S. patent application Ser. No.09/970,197 filed on Oct. 3, 2001 and entitled “Manufacturing Method AndComposite Powder Metal Rotor Assembly For Induction Machine”; U.S.patent application Ser. No. 09/970,223 filed on Oct. 3, 2001 andentitled “Manufacturing Method And Composite Powder Metal Rotor AssemblyFor Surface Type Permanent Magnet Machine”; U.S. patent application Ser.No. 09/970,105 filed on Oct. 3, 2001 and entitled “Manufacturing MethodAnd Composite Powder Metal Rotor Assembly For Circumferential TypeInterior Permanent Magnet Machine”; and U.S. patent application Ser. No.09/970,106 filed on Oct. 3, 2001 and entitled “Manufacturing Method AndComposite Powder Metal Rotor Assembly For Spoke Type Interior PermanentMagnet Machine,” each of which is incorporated by reference herein inits entirety. Additionally, the following co-pending application isdirected to composite powder metal electric machine rotor coresfabricated by metal injection molding: U.S. patent application Ser. No.09/970,226 filed on Oct. 3, 2001 and entitled “Metal Injection MoldingMultiple Dissimilar Materials To Form Composite Electric Machine RotorAnd Rotor Sense Parts,” incorporated by reference herein in itsentirety. Both the compaction-sinter process and the metal injectingmolding process (as disclosed in the above-referenced patentapplications) lead to the advantages described above, such as strongstructural support and virtually non-existent permeable flux leakagepaths, and do provide an opportunity to manufacture an electric machinethat costs less, spins faster, provides more output power, and is moreefficient.

In the compaction-sinter process described in the above-identifiedco-pending applications, the magnetic and non-magnetic metal powders arepoured into respective sections of a disk-shaped die insert. Uponremoval of the die insert, the powders, after some settling and mixingalong their boundaries, are compressed to a “green” strength, which isusually on the order of 2–6 ksi (13.8–41.4 MPa). The green part is thensintered, such as at about 2050° F. (1121° C.), for about one hour toobtain full strength, typically on the order of 30–50 ksi (207–345 MPa).One disadvantage of this compaction process is that the mixing thatoccurs after the die insert is removed can lead to blurred boundariesbetween permeable and non-permeable materials thereby reducingperformance. Further, the blurring of boundaries is often particularlypronounced near the top and bottom of the pressed disks such that thesesections of the machine do not adequately perform their intendedfunction. To overcome this disadvantage, approximately one-third totwo-thirds of the disk's thickness is ground away to leave a middlesection having minimal blurring of boundaries that can be effectivelyutilized as an electric machine component.

The composite metal injection molding process described in theabove-identified co-pending application does not exhibit the problem ofboundary blurring like the composite compaction-sintering manufacturingprocess because the magnetic and non-magnetic materials areinjection-molded separately into molds that provide definitive edges.However, the injection molding process can be expensive becauseliquifying the metals generally requires the use of powders that aremore expensive and of finer grain size than the powders that can be usedin the compaction process. Thus, composite metal injection molding maynot be cost effective for a broad range of electric machineapplications.

There is thus a need to provide a powder metallurgy manufacturingprocess that is cost effective and provides definitive boundariesbetween magnetic (permeable) and non-magnetic (non-permeable) portionsof the electric machine components.

SUMMARY OF THE INVENTION

The present invention provides a method of making composite electricmachine components using powder metal for magnetic and non-magneticportions of the component. To this end, and in accordance with thepresent invention, one or more magnetically conducting segments areformed to a green strength by pressing soft ferromagnetic powder metalin a die of desired shape. Similarly, one or more magneticallynon-conducting segments are formed to a green strength by pressingnon-ferromagnetic powder metal in a die of desired shape. The greenstrength segments are positioned adjacent each other in a desiredmagnetic pattern, and powder metal is added between adjacent segments.The assembly is then sintered, advantageously to full strength, wherebya bond is formed between segments by the added powder metal.

In an exemplary embodiment for forming a rotor assembly, the segmentsare positioned to form a disk having the desired magnetic pattern, and aplurality of sinterbonded disks are stacked on a shaft with theirmagnetic patterns aligned. In an embodiment of the present invention,permanent magnets may be affixed to the composite component to form apermanent magnet electric machine component. Alternatively, permanentmagnet segments may be formed to a green strength by pressing hardferromagnetic powder metal in a die of desired shape, and then placingthe permanent magnet segments in the desired magnetic pattern followedby sintering and magnetizing to form a permanent magnet electric machinecomponent. By the method of the present invention, there is provided astructurally robust electric machine component having definiteboundaries between magnetic regions that costs less, spins faster,provides more output power, and is more efficient.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIG. 1 is a perspective view of a sinterbonded powder metal surface typepermanent magnet rotor assembly of the present invention having a rotorpositioned on a shaft, the rotor comprising a plurality of sinterbondeddisks;

FIG. 2 is a partially exploded plan view of a partially assembled diskfor the rotor assembly of FIG. 1 prior to sinterbonding;

FIG. 2A is an enlarged view of encircled area 2A of FIG. 2;

FIG. 3A is a partially exploded plan view of a partially assembled diskfor a sinterbonded powder metal switched reluctance rotor assembly priorto sinterbonding;

FIG. 3B is a perspective view of the assembled and sinterbonded disk ofFIG. 3A;

FIG. 4A is an exploded plan view of a disassembled disk for asinterbonded powder metal synchronous reluctance rotor assembly prior tosinterbonding;

FIG. 4B is a plan view of the assembled and sinterbonded disk of FIG.4B;

FIG. 5A is an exploded perspective view of a disassembled disk for asinterbonded powder metal induction rotor assembly prior tosinterbonding and prior to adding the rotor conductors;

FIG. 5B is a plan view of the assembled disk of FIG. 5A aftersinterbonding;

FIG. 5C is a plan view of a rotor assembly including the disk of FIG. 5Bafter adding the rotor conductors;

FIG. 6A is a partially exploded plan view of a partially assembled diskfor a sinterbonded powder metal spoke type interior permanent magnetrotor assembly prior to sinterbonding;

FIG. 6B is a plan view of the assembled and sinterbonded disk of FIG.6A;

FIG. 7A is an exploded plan view of a disassembled disk for asinterbonded powder metal circumferential type interior permanent magnetrotor assembly prior to sinterbonding; and

FIG. 7B is a plan view of the assembled and sinterbonded disk of FIG.7A.

DETAILED DESCRIPTION

The present invention is directed to sinterbonding electric machinecomponents by pressing magnetically conducting and magneticallynon-conducting rotor or stator segments separately to a green state,arranging the green-strength segments adjacent to each other with asmall amount of powder material in between green-strength segments, andthen sintering the whole assembly. The small amount of powder material,such as high purity iron powder, facilitates bond formation between theseparate green-strength segments during sintering. By way of example andnot limitation, the sinterbonding process of the present invention maybe used on induction, permanent magnet, switched reluctance andsynchronous reluctance rotors, as well as permanent magnet and reluctantsensor wheels. Sinterbonding combines the cost advantage of compositepowder metal compaction manufacturing processing with the performanceadvantage of metal injection molding processing by allowing themagnetically conducting and magnetically non-conducting electric machinesegments to be pressed separately and then bonded together during thesintering process. The sinterbonded product yields bond strengths equalto either of the prior powder metal processes, while at the same timereducing tooling costs because the tooling only has to be large enoughto accommodate the individual segments and not the whole rotor or statorcomponent. For example, on a ring machine used for an integral-startergenerator application, the tooling for compaction or molding processesmust be large enough to construct a 360 mm outer diameter core, whereaswith the sinterbonding of the present invention, the largest toolingrequired would be for a 50 mm wide by 20 mm thick part.

An additional advantage of sinterbonding in accordance with the presentinvention is that less post-machining is required than with compositepowder metal compaction-sinter processes. During material fill for thecompaction-sinter process, the permeable and non-permeable materials maydetrimentally mix along their boundaries prior to compaction,particularly near the top and bottom of the rotor disks. After the disksare sintered, the tops and bottoms often must be ground to leave onlypermeable and non-permeable materials that are clearly bonded togetherbut distinct from each other. With sinterbonding, the materials arealways distinct from each other because they are pressed separately,then sintered together. Thus, the sinterbonding process of the presentinvention eliminates the need for extensive bottom and top grinding ofthe disks that comprise the rotor or stator assembly. In addition,sinterbonding is less expensive than metal injection molding because itdoes not require the finer and more expensive powders generally requiredto liquify for the injection molding process.

Composite powder metal parts, whether they are compacted orinjection-molded as described in the co-pending applications referred toabove or whether they are sinterbonded in accordance with the presentinvention, have a cost, strength and performance advantage overtraditional stamped electric machine cores. Composite powder metalcomponents are less expensive because they can be formed in greaterpiece thicknesses and can be formed into near-net shape parts withlittle or no scrap material. Composite powder metal cores are strongerthan traditional stamped electric machine cores because most electricmachine components must minimize the use of non-permeable materials usedas structural elements to avoid flux leakage and lower machineperformance, whereas composite powder metal components may utilizerelatively large amounts of non-permeable material, for examplestainless steel, for the structural elements while minimizing oreliminating the magnetic flux leakage pathways. With less or no fluxleakage, they also perform better in terms of output power, power factorand efficiency. By way of example, a four-inch diameter induction rotorcomprising stamped laminations and aluminum bars and end rings, whensubjected to spin testing, fails at about 28,000 rpm, whereas afour-inch diameter synchronous reluctance rotor of the present inventiondoes not fail until about 44,600 rpm. Thus, the sinterbonding process ofthe present invention reduces tooling costs and produces electricmachine components that are less expensive, stronger, faster and moreefficient than those produced by prior techniques.

In general, a rotor assembly comprises an annular core having at leastone magnetically conducting segment and at least one magneticallynon-conducting segment. The magnetically conducting segments comprisesoft ferromagnetic materials, also referred to as permeable or magneticmaterials. The magnetically non-conducting segments comprisenon-ferromagnetic material, also referred to as non-permeable ornon-magnetic materials. In the present invention, the magneticallyconducting segments and magnetically non-conducting segments arefabricated from pressed and sintered soft ferromagnetic andnon-ferromagnetic powder metals. In permanent magnet rotor assemblies,the assembly further comprises permanent magnets, which are formed fromhard ferromagnetic materials. In the present invention, the permanentmagnets may be formed from pressed and sintered hard ferromagneticpowder metal, or may be prefabricated magnets that are affixed to thesinterbonded component. In induction rotor assemblies, the assemblyfurther comprises conductors that are generally made of aluminum orcopper. For example, aluminum conductors may be cast into slots in thesinterbonded rotor assembly, or prefabricated copper bars may beinserted into the slots and affixed to axial end rings.

The electric machine components may be fabricated by sinterbondingmagnetically conducting and magnetically non-conducting segments to forma plurality of composite disks of a desired magnetic pattern, andstacking the disks axially along a shaft and affixing the disks to theshaft to form the rotor assembly. The shaft is typically equipped with akey and the individual disks have a keyway on an interior surface tomount the disks to the shaft upon pressing the part to the shaft. Themagnetic patterns of the individual disks are aligned with respect toeach other along the shaft such that the magnetic flux paths are alignedalong the shaft. In the present invention, there is no limit to thethickness of each composite powder metal disk or the number of disksthat may be utilized to construct a rotor assembly.

In an embodiment of the present invention, the soft ferromagnetic powdermetal used to form magnetically conducting segments is nickel, iron,cobalt or an alloy thereof. In another embodiment of the presentinvention, this soft ferromagnetic metal is a low carbon steel or a highpurity iron powder with a minor addition of phosphorus, such as coveredby MPIF (Metal Powder Industry Federation) Standard 35 F-0000, whichcontains approximately 0.27% phosphorus. In general, AISI 400 seriesstainless steels are magnetically conducting, and may be used in thepresent invention.

In an embodiment of the present invention, the non-ferromagnetic powdermetal used to form magnetically non-conducting segments is austeniticstainless steel, such as SS316. In general, the AISI 300 seriesstainless steels are non-magnetic and may be used in the presentinvention. Also, the AISI 8000 series steels are non-magnetic and may beused.

In an embodiment of the present invention, the soft ferromagnetic metaland the non-ferromagnetic metal are chosen so as to have similardensities and sintering temperatures, and are approximately of the samestrength, such that upon compaction and sinterbonding, the materialsbehave in a similar fashion. In an embodiment of the present invention,the soft ferromagnetic powder metal is Fe-0.27%P and thenon-ferromagnetic powder metal is SS316.

In an embodiment of the present invention, the small amount of powdermetal added between the green-strength segments is a soft ferromagneticmaterial, such as described above. For example, the small amount ofadded powder metal may be high purity iron powder, such as covered byMPIF Standard 35 F-0000. In another embodiment of the present invention,the small amount of added powder metal is the same powder metal as usedto form the magnetically conducting segments of the rotor or statorcomponents. Alternatively, the small amount of added powder metal may bea non-ferromagnetic material, such as described above. For example, thesmall amount of added powder metal may be an austenitic stainless steel,such as SS316. In yet another embodiment of the present invention, thesmall amount of added powder metal is the same powder metal as used toform the magnetically non-conducting segments of the rotor or statorcomponents.

In an embodiment of the present invention relating to permanent magnetmachines, the hard ferromagnetic powder metal used to form permanentmagnet segments is ferrite or rare earth metals. Alternatively, thepermanent magnets may be prefabricated magnets that are affixed toadjacent segments in the rotor component after sinterbonding.

In accordance with the present invention, the ferromagnetic andnon-ferromagnetic powder metals are pressed separately in individualdies to form the compacted powder metal segments, or green-strengthsegments. The compacted powder metal segments are then positionedadjacent to each other in the desired magnetic pattern. A small amountof powder metal is then provided between the green-strength segments,and the arrangement is then sintered to form a sinterbonded powder metalcomponent or lamination having at least one region of magneticallynon-conducting material and at least one region of magneticallyconducting material, the component exhibiting high structural stabilityand definitive boundaries between regions. The component may be anannular disk-shaped component for affixing to a shaft to form a rotorassembly. The amount of powder metal provided between green-strengthsegments may be any amount deemed necessary or adequate for a bond toform between the segments.

The pressing or compaction of the filled powder metal to form thegreen-strength segments may be accomplished by uniaxially pressing thepowder in a die, for example at a pressure of about 45–50 tsi (620–689MPa). The die is shaped to correspond to the particular segment beingfabricated. It should be understood that the pressure needed isdependent upon the particular powder metal materials that are chosen. Ina further embodiment of the present invention, the pressing of thepowder metal involves heating the die to a temperature in the range ofabout 275° F. (135° C.) to about 290° F. (143° C.), and heating thepowder within the die to a temperature in the range of about 175° F.(79° C.) to about 225° F. (107° C.).

In an embodiment of the present invention, the sintering together of thegreen-strength segments with added powder therebetween comprises heatingthe green-strength segments and added powder metal to a firsttemperature of about 1400° F. (760° C.) and holding at that temperaturefor about one hour. Generally, the powder metals used to fabricate thesegments include a lubricating material, such as a plastic, on theparticles to increase the strength of the material during compaction.The internal lubricant reduces particle-to-particle friction, thusallowing the compacted powder to achieve a higher strength aftersintering. The lubricant is then burned out of the composite during thisinitial sintering operation, also known as a delubrication or delubingstep. A delubing for one hour is a general standard practice in theindustry and it should be appreciated that times above or below one hourare sufficient for the purposes of the present invention ifdelubrication is achieved thereby. Likewise, the temperature may bevaried from the general industry standard if the ultimate delubingfunction is performed thereby.

After delubing, the sintering temperature is raised to a full sinteringtemperature, which is generally in the industry about 2050° F. (1121°C.). During this full sintering, the compacted powder shrinks, andparticle-to-particle bonds are formed, generally between iron particles.For the particles that comprise the small amount of powder metal addedbetween green-strength segments, the particles bond to each other and toparticles that comprise the magnetically conducting and non-conductingsegments to thereby bond the segments to each other. Standard industrypractice involves full sintering for a period of one hour, but it shouldbe understood that the sintering time and temperature may be adjusted asnecessary. The sintering operation may be performed in a vacuum furnace,and the furnace may be filled with a controlled atmosphere, such asargon, nitrogen, hydrogen or combinations thereof. Alternatively, thesintering process may be performed in a continuous belt furnace, whichis also generally provided with a controlled atmosphere, for example ahydrogen/nitrogen atmosphere such as 75% H₂/25% N₂. Other types offurnaces and furnace atmospheres may be used within the scope of thepresent invention as determined by one skilled in the art.

The sinterbonded powder metal components of the present inventiontypically exhibit magnetically conducting segments having at least about95% of theoretical density, and typically between about 95%–98% oftheoretical density. Wrought steel or iron has a theoretical density ofabout 7.85 gms/cm³, and thus, the magnetically conducting segmentsexhibit a density of around 7.46–7.69 gms/cm³. The non-conductingsegments of the powder metal components of the present invention exhibita density of at least about 85% of theoretical density, which is on theorder of about 6.7 gms/cm³. Thus, the non-ferromagnetic powder metalsare less compactable than the ferromagnetic powder metals. The pressedand sintered hard ferromagnetic powder metal magnets of certainembodiments of the present invention exhibit a density of at least95.5%± about 3.5% of theoretical density, depending on fill factor,which is on the order of about 3.8–7.0 gms/cm³. The sinterbonding methodfor forming these rotor components provides increased mechanicalintegrity, reduced flux leakage, more efficient flux channeling, reducedtooling cost, and simpler construction.

To further explain the method of the present invention and the compositepowder metal components formed thereby, reference is made to thefollowing figures in which there are depicted exemplary components forvarious electric machines. The components depicted are by no meansexhaustive of the range of applicability of the present invention. Allgreen-strength segments described in reference to the figures arefabricated individually by compacting an appropriate powder metal in adie having the desired segment shape, as described above.

FIG. 1 depicts in perspective view a powder metal surface permanentmagnet rotor assembly 10 of the present invention having a plurality ofsinterbonded powder metal composite disks 12 aligned and mounted on ashaft 14, the disks 12 each having an inner annular magneticallyconducting segment 16 and a plurality of spaced magneticallynon-conducting segments 18 separated by a plurality of alternatingpolarity permanent magnets 20. The magnetically non-conducting segments18 provide insulation that in part directs the magnetic flux from onepermanent magnet 20 to the next alternating polarity permanent magnet20.

A partially assembled, unsintered disk 12 a is depicted in FIG. 2 in apartially exploded plan view. The inner annular segment 16 is formed bycompacting a soft ferromagnetic powder metal in a die to form agreen-strength conducting segment 16 a. The magnetically non-conductingsegments 18 are each formed by compacting a non-ferromagnetic powdermetal in a die to form green-strength non-conducting segments 18 a. Inthe particular embodiment of the present invention depicted in FIG. 2,the permanent magnets 20 are each formed by compacting a hardferromagnetic powder metal in a die to form green-strength permanentmagnets 20 a. The alternating polarity may be created aftersinterbonding. The green-strength magnetically non-conducting segments18 a and green-strength permanent magnet segments 20 a are placedadjacent the green-strength inner annular magnetically conductingsegment 16 a in alternating relation, as indicated by the arrows. FIG.2A depicts, in an enlarged view, a portion of disk 12 a to show thegreen-strength segments 16 a, 18 a, 20 a that are individuallyfabricated and then positioned adjacent each other with powder metal 22added between segments for sintering to form the sinterbonded disk 12 ofFIG. 1. Alternatively, the permanent magnets 20 may be prefabricatedmagnets that are added after sinterbonding green-strength magneticallynon-conducting segments 18 a to green-strength magnetically conductingsegment 16 a. Spacing inserts (not shown) may be temporarily placedbetween segments 18 a to facilitate proper positioning around segment 16a. The inserts are removed, and prefabricated magnets 20 may then beadhesively affixed to sinterbonded segments 18 and/or 16.

FIG. 3A depicts in partially exploded plan view a partially assembledunsintered disk 30 a for a composite powder metal switched reluctancerotor assembly of the present invention (not shown). The disk 30 aincludes a green-strength magnetically conducting segment 32 a that hasa yoke portion 34 a and a plurality of equiangular spaced, radiallyextending teeth 36 a defining channels there between. Green-strengthmagnetically non-conducting segments 38 a are placed, as indicated bythe arrows, in the channels between the teeth 36 a. Added powder metal(not shown) is added between adjacent segments 32 a and 38 a. Thesegments are then subjected to sintering to bond the segments together.FIG. 3B depicts in perspective view the fully assembled and sintereddisk 30 from FIG. 3A having magnetically non-conducting segments 38sinterbonded to magnetically conducting segment 32. A plurality of disks30 may be affixed to a shaft to form a rotor assembly. Thenon-conducting segments 38 function to cut down on windage losses, andmore particularly, a switched reluctance machine incorporating thepowder metal rotor disks 30 of the present invention exhibits lowwindage losses as compared to assemblies comprising stamped laminations.

FIG. 4A depicts in partially exploded plan view an unassembled,unsintered disk 40 a for a composite powder metal synchronous reluctancerotor assembly of the present invention (not shown). The disk 40 aincludes a plurality of alternating green-strength magneticallyconducting arcuate segments 42 a and non-conducting arcuate segments 44a, which are placed, as indicated by the arrows, in stacked arrangementsadjacent a green-strength magnetically non-conducting segment 46 a. Thissegment 46 a essentially forms four equiangular spaced, radiallyextending arm portions 48 a that define axially extending channels therebetween, in which segments 42 a, 44 a, are alternately placed. Addedpowder metal (not shown) is added between adjacent segments 42 a, 44 a,and 46 a. The segments are then subjected to sintering to bond thesegments together. FIG. 4 b depicts in plan view the fully assembled andsintered disk 40 from FIG. 4A having magnetically non-conducting segment46 with arm portions 48 forming channels, and within those channels arealternating layers of magnetically conducting segments 42 andmagnetically conducting segments 44. It should be understood, however,that a disk for a synchronous reluctance rotor assembly may be formed ofan opposite magnetic pattern in which the segment having the armportions may be conducting, with alternating magnetically non-conductingsegments and magnetically conducting segments in the channels. A varietyof other magnetic configurations are known and well within the skill ofone in the art. A plurality of disks 40 may be affixed to a shaft toform a powder metal rotor assembly. A synchronous reluctance machineincorporating the powder metal rotor disks 40 of the present inventionexhibits power density and efficiency comparable to induction motors andimproved high speed rotating capability, yet may be produced at a lowercost.

FIG. 5A depicts in partially exploded perspective view an unassembled,unsintered disk 50 a for a composite powder metal induction rotorassembly of the present invention (not shown), the disk 50 a having agreen-strength magnetically conducting segment 52 a and a plurality ofslots or slot openings 54 extending along the axial length of thesegment 52 a for receiving a plurality of conductors 55. Agreen-strength magnetically non-conducting segment 56 a is placed ineach slot 54, as indicated by the arrow, to thereby cap or enclose theslot opening 54. Powder metal (not shown) is added between adjacentsegments 52 a and 56 a, and the segments are then subjected to sinteringto bond the segments together. FIG. 5B depicts in plan view a fullyassembled and sintered disk 50 from FIG. 5A having a magneticallyconducting segment 52 with spaced axially extending slots 54 around theexterior surface of the segment 52 for receiving a plurality ofconductors 55, and magnetically non-conducting segments 56 enclosingeach slot opening 54 adjacent the exterior surface of the segment 52. Aplurality of disks 50 may be affixed to a shaft 58 with the slots 54aligned axially along the shaft, and conductors 55 are then added in thealigned slots 54, as indicated by the arrow in FIG. 5A, to form acomposite powder metal rotor assembly 59, as depicted in FIG. 5C. Theconductors 55 may be cast into the aligned slots 54 of the compositedisks 50 or may be prefabricated bars inserted into the slots 54. Thus,each slot 54 receives a conductor 55 in a radially inner portion of theslot 54, and a radially outer portion of the slot 54 comprises thenon-conducting segment 56 such that the conductors 55 are embeddedwithin the rotor assembly 59. An induction machine incorporating thepowder metal rotor assembly 59 of the present invention can obtain highspeeds with low flux leakage, and yet may be produced at a lower cost.

FIG. 6A depicts in partially exploded plan view a partially assembled,unsintered disk 60 a for a composite powder metal spoke type interiorpermanent magnet rotor assembly of the present invention (not shown).The disk 60 a includes an inner annular green-strength magneticallynon-conducting segment 62 a around which is placed, as indicated by thearrows, a plurality of green-strength permanent magnet segments 64 aseparated by green-strength magnetically conducting segments 66 a. Aradially outer green-strength magnetically non-conducting segment 68 ais placed adjacent each permanent magnet segment 64 a for embedding thepermanent magnet segment 64 a in the disk 60 a. Powder metal (not shown)is added between adjacent segments 62 a, 64 a, 66 a and 68 a. Thesegments are then subjected to sintering to bond the segments together.FIG. 6B depicts in plan view the fully assembled and sintered disk 60from FIG. 6A having an inner annular magnetically non-conducting segment62, a plurality of alternating polarity permanent magnets 64 (polarizedsubsequent to sinterbonding) separated by magnetically conductingsegments 66 and radially embedded by magnetically non-conductingsegments 68. Two adjacent permanent magnets 64 direct their magneticflux into the intermediate conducting segment 66, which forms one rotorpole, and the next adjacent rotor pole will be of opposite polarity. Aswith FIG. 2 above, permanent magnets 64 are depicted as compacted andsinterbonded hard ferromagnetic powder metal segments, but mayalternatively be prefabricated and affixed to adjacent segments aftersinterbonding. A plurality of disks 60 may be affixed to a shaft to forma powder metal rotor assembly. A spoke type interior permanent magnetmachine incorporating the powder metal rotor disks 60 of the presentinvention exhibits flux concentration, minimal flux leakage and permitsthe motor to produce more power than a circumferential interiorpermanent magnet motor or to produce the same power using less powerfuland less expensive magnets, and may be produced at a lower overall cost.

FIG. 7A depicts in exploded plan view an unassembled, unsintered disk 70a for a composite powder metal circumferential type interior permanentmagnet rotor assembly of the present invention (not shown). Disk 70 aincludes a green-strength inner annular magnetically conducting segment72 a, around which is placed, as indicated by the arrows, a plurality ofgreen-strength permanent magnet segments 74 a and a plurality ofgreen-strength magnetically non-conducting barrier segments 76 a forseparating the permanent magnet segments 74 a. A plurality of radiallyouter green-strength magnetically conducting segments 78 a are placedadjacent each permanent magnet segment 74 a for embedding the permanentmagnet 74 a in the disk 70 a. FIG. 7A further depicts placing anoptional green-strength inner annular magnetically non-conducting insert80 a within segment 72 a. Added powder metal (not shown) is addedbetween adjacent segments 72 a, 74 a, 76 a, 78 a and 80 a. The segmentsare then subjected to sintering to bond the segments together. FIG. 7Bdepicts in plan view the fully assembled and sintered disk 70 from FIG.7A having an inner annular magnetically conducting segment 72 and aninner annular magnetically non-conducting insert 80 therein. Positionedaround segment 72 is a plurality of circumferentially extendingalternating polarity permanent magnets 74 (polarized aftersinterbonding) separated in between by magnetically non-conductingbarrier segments 76. The non-conducting segments 76 provide insulationthat in part directs the magnetic flux from one permanent magnet 74 tothe next alternating polarity permanent magnet 74. The insert 80 blocksmagnetic flux from being channeled into the shaft (not shown) when therotor assembly (not shown) is operating. The permanent magnets 74 arealso circumferentially embedded by radially outer magneticallyconducting segments 78. As with FIG. 2 above, the permanent magnets aredepicted as compacted and sinterbonded hard ferromagnetic powder metalsegments, but may alternatively be prefabricated magnets affixed toadjacent segments after sinterbonding. A plurality of disks 70 may beaffixed to a shaft to form a powder metal rotor assembly. Acircumferential type interior permanent magnet machine incorporating thepowder metal rotor disks 70 of the present invention exhibits increasedpower and speed capabilities, lower flux leakage, and may be produced ata lower cost.

While the present invention has been illustrated by the description ofone or more embodiments thereof, and while those embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The invention in its broader aspects is thereforenot limited to the specific details, representative apparatus and methodand illustrative examples shown and described. Accordingly, departuresmay be made from such details without departing from the scope or spiritof applicant's general inventive concept.

1. A method of making a composite electric machine rotor assembly of adesired magnetic pattern, the method comprising: forming at least onegreen-strength magnetically conducting segment by pressing a softferromagnetic powder metal in a die; forming at least one green-strengthmagnetically non-conducting segment by pressing a non-ferromagneticpowder metal in a die; placing the green-strength magneticallyconducting segments adjacent the magnetically non-conducting segments toform a disk in the desired magnetic pattern; adding powder metal betweenthe segments; and sintering the segments and added powder metal wherebythe segments are bonded together by the added powder metal to form asinterbonded composite disk; stacking a plurality of the sinterbondedcomposite disks axially on a shaft with the magnetic patterns aligned toform the composite electric machine rotor assembly.
 2. The method ofclaim 1 wherein the added powder metal is the soft ferromagnetic powdermetal.
 3. The method of claim 1 wherein the added powder metal is thenon-ferromagnetic powder metal.
 4. The method of claim 1 wherein thesoft ferromagnetic powder metal is Ni, Fe, Co or an alloy thereof. 5.The method of claim 1 wherein the soft ferromagnetic powder metal is ahigh purity iron powder with a minor addition of phosphorus.
 6. Themethod of claim 1 wherein the non-ferromagnetic powder metal is anaustenitic stainless steel.
 7. The method of claim 1 wherein thenon-ferromagnetic powder metal is an AISI 8000 series steel.
 8. Themethod of claim 1 wherein pressing comprises uniaxially pressing thepowder in the die.
 9. The method of claim 8 wherein pressing comprisespre-heating the powder and pre-heating the die.
 10. The method of claim1 wherein sintering includes delubricating the segments by heating to afirst temperature, followed by fully sintering the segments by heatingto a second temperature greater than the first temperature.
 11. Themethod of claim 1 further comprising forming at least one green-strengthpermanent magnet segment by pressing a hard ferromagnetic powder metalin a die, placing the green-strength permanent magnet segments adjacentthe magnetically conducting segments and magnetically non-conductingsegments in the desired magnetic pattern, and after sintering,magnetizing the permanent magnet segments to form thereby a permanentmagnet type electric machine rotor assembly.
 12. The method of claim 1further comprising, after sintering, adding a plurality of alternatingpolarity permanent magnets to the composite disk to thereby form apermanent magnet electric machine rotor assembly.